(a) Field of the Invention
The present invention relates to a display device and a driving method thereof.
(b) Description of the Related Art
A liquid crystal display (“LCD”) includes a pair of panels provided with field generating electrodes, and a liquid crystal (“LC”) layer disposed between the two panels and having dielectric anisotropy. The field generating electrodes generally include a plurality of pixel electrodes on one of the panels arranged in a matrix and connected to switching elements such as thin film transistors (“TFTs”) to be supplied with data voltages for every row, and a common electrode on the other panel covering an entire surface of the panel and supplied with a common voltage. A pair of field generating electrodes that generate the electric field in cooperation with each other and a liquid crystal disposed therebetween form a so-called liquid crystal capacitor that is a basic element of a pixel along with a switching element.
The LCD has a frame frequency of about 60 Hz, and applies the voltages to the field generating electrodes to generate an electric field to the liquid crystal layer, and the strength of the electric field can be controlled by adjusting the voltage across the liquid crystal capacitor. Since the electric field determines orientations of liquid crystal molecules within the liquid crystal layer and the molecular orientations determine the transmittance of light passing through the liquid crystal layer, the light transmittance is adjusted by controlling the applied voltages, thereby obtaining desired images.
In order to prevent image deterioration due to long-term application of the unidirectional electric field, etc., polarity of the data voltages with respect to the common voltage is reversed every frame, every row, or every pixel.
Polarity inversion of the data voltages increases the charging time of the liquid crystal capacitor because of the response time of the liquid crystal. Therefore, it takes a relatively long time for the liquid crystal capacitor to reach a target luminance (or target voltage) such that an image displayed by the LCD is unclear and blurred.
In order to solve this problem, impulsive driving that inserts a black image for a short time between normal images has been developed.
Impulsive driving includes an impulsive emission type of driving that periodically turns off a backlight lamp to yield black images, and a cyclic resetting type of driving that periodically applies a black data voltage for making the pixels become a black state between the applications of normal data voltages to the pixels.
However, these techniques cannot compensate the large response time of the liquid crystal, and the response time of the backlight lamp is relatively large as well. Therefore, afterimages and flickering are generated which deteriorates image quality. In addition, the cyclic resetting type of driving may decrease the time for applying normal data voltages for displaying normal images such that the liquid crystal capacitors do not reach a target luminance, and thus an image displayed by the LCD is unclear and blurred.